12V Battery Died after a surprisngly short time...

Well, I've only had my Prime for about 14 months, but I've never heard any fan run when the car is off and it isn't being charged. If fact, if I've been driving in hot weather, I'll often hear the fans running when I stop the car. (Prime & PiP have two battery fans.) When I shut off the car, the fans stop. I'd rather they ran a little while like the radiator fan did on my last motorcycle when I shut it off.

 

mendel has it right. it runs about four hours after shutting the car down. not sure for how long, never timed it.

many people have commented on it over the years. i'm not sure prime has it, just assuming.

but other than that, i can't think of anything the 12v would run with the car off, except the usual suspects

 

1. no, I usually hear the fan in afternoon when the car is off and the traction battery charger is plugged in but not actively charging. My routine is to plug in charger when turn off car but set it to be charged by 7:00 next morning.
2. If a fan is operating, it would be 12 volt and drawing down the 12 volt battery unless the car was in ready or perhaps being actively charged.

 

I like that this is actually on page 8 of the manual. According to one of my mom's stock phrases, that would mean Mendel does know his @ss from page 8. (The phrase is usually about somebody who doesn't.)

 

From all the information available, I really don't think what you heard is the traction battery cooler fan running. There is no mention in the manual that this fan running when the hybrid system is off and not being charged. Even if it was the traction battery fan, it would be hard to believe, the fan would run from traction battery power in one operation mode and then from 12v power source in a different time. A fuel evaporation leakage check mentioned above maybe the noise you heard. That I believe only happens once after you turn off the car, not every day, and having the 12v battery disconnected would not hurt the car if this function is not running.

That being said, I do not like the idea of disconnecting 12v, for it would erase some data in ECU and requires re-initialization when you re-connect. Keeping the 12v battery connected and putting it on a maintainer would be preferable.

 

according to o/p's post 59, he's not going to buy anything aftermarket, so, short of running the car often enough to keep the 12v charged, disconnecting the neg until the car is needed may be worth having to reset a few unimportant functions.

 

You have no way of knowing what is REALLY happening with the batteries and charging at a time like that.
If it is plugged in, it could be supplying 12 V charging current without telling you about it.
Assumptions are often wrong.

 

it has been established that a minimum amount of charging of the 12v takes place while the hybrid battery is wall charging. much less than the pip, for what reason has not been established.

 

I'm sure that's true. But that would make this car behave differently than other cars in that regard. That would lead to unnecessary confusion.

 

Grab a float/ smart charger and connect it to the battery once a week and let it fully charge. That's what I have been doing

 

I recommend getting a charger.

 

Ive been using this with good luck

https://tinyurl.com/y89vbqjo

 

You don't have to actually drive the car. All you need is to start the car and let it sit at READY. If you charge up the traction battery prior to this, then the car does not need to run engine at all. In my experience with my 2020 PRIME, almost brand new 12v battery, 1-1.5hr once a week keeps the 12v battery charge above 12.4v, but each week, the SoC would be bit lower after charge. After 3 weeks, the resting voltage got lower than 12.3v, so I charged the battery fully using a smart charger. With your 3 years old battery that has been deeply discharged more than once, you may need more frequent and/or longer charges. If I were you, just buy a battery tender/maintainer and hook it up until you need to drive the car again.

 

We're driving (our 2010 Prius) very infrequently, often just once a week. On the day after it's been driven I hooked it up to a smart charger (CTEK 4.3), in the car (no removal), and leave it connect 'till next time the car is needed.

For convenience I've installed a quick connect, so I'm not dealing with alligator clips: make the connection, plug charger into wall, lower the hood, just ajar. I do have a secure garage, which helps.

 

I'm singing in the battery charger chorus, too. Sure, you can put it in ready now and then and charge it back up. If you remember. And then you have to check & see if it's charged enough. Royal pain in the patootie. Just hook up a battery tender type charger and get on with life.

 

Yep!

 

If I were you.......that would have been the FIRST sentence in my post instead of the last.

And for the OP: Just because a shop tells you your battery is "good" doesn't necessarily mean that is true.